.box{
    width: 100%;
    height: 900px;
}
.box>.left{
    width: 200px;
    height: 100%;
    background-color: #2d3d51;
    color: #fff;
    padding: 20px;
}
.box>.left>.title{
    font-size: 17px;
    font-weight: 700;
    margin: 10px;
}
.box>.left>ul li{
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 50px;
    line-height: 50px;

}
/* 修改 */
.box>.left>ul .li{
    display: inline-block;
    width: 8px;
    height: 8px;
    content: '';
    transform: rotate(45deg);
    transition: 0.3s;
    border-top: 1px solid #ccc;
    border-right: 1px solid #ccc;
}

.box>.left>ul li>a{
    font-size: 15px;
    color: #ccc;
}
.box>.left>ul li .active{
    color: rgb(27, 135, 236);
}

/* 后添加 */
.two-ul{
    margin-left: 20px;
    height: 0;
    overflow: hidden;
    transition: 0.5s;
}
.two-ul a::before{
    content: '';
    display: inline-block;
    width: 10px;
    height: 10px;
    background-color:#1b87ec;
    margin-right: 10px;
    border-radius: 50%;
}